# Question about redshift and effective gravity at the rotating neutron star surface

For a rapidly rotating neutron star, if consider the star as a sphere, redshift at the equator surface will be larger than at the pole. But if consider the star as an obsolate sphereiod (the ellipsoid varies according to the rotation velocity), then how about the redshift at equator compare to the pole surface? Whether the obsolate decrease the redshift at equator? Similar is the effective gravity, if consider the obsolate effect, how about the gravity difference between the equator and the pole compare to that a sphere?

• Why would the redshift at the equator be larger than at the pole for a spherical star? Dec 4 '20 at 16:51
• Imagine a rotating sphere. Its equator partially blueshifted, partially redshifted, depending on the angle. Its pole is not shifted in any direction (by doppler, there is still a gravitational redshift due to its gravity). How this differs if the star is an oblate spheroid? I think, it does not. Please extend your question to make it more clear. Dec 4 '20 at 18:38
• But @peterh-ReinstateMonica that is a variable Doppler shift, not a redshift. Dec 5 '20 at 0:26
• From this paper: arxiv.org/pdf/1310.0987.pdf you can see that the redshift is latitude dependent for a rotating neutron star.
– Chen
Dec 5 '20 at 9:34
• BTW, not all fast spinning neutron stars are necessarily oblate spheroids. There is evidence to suggest that the extremely intense magnetic fields of magnetars can squeeze them into prolate spheroids, as I mentioned here. Dec 5 '20 at 15:17